In order to remove the border around your arrow image, simply add the following CSS rule:
In order to fix the bottom margins in IE, please try changing the vertical alignment of the arrow image.
As for the missing background, this problem is caused by an uncleared float. When an element contains only floated children, there is nothing to expand it vertically (in IE the behavior is different). In order to fix this, you have to clear the float by using the following technique:
SomeClass is the CSS class of the parent, which contains floated elements.
If you still have troubles making the custom skins work, please send them to us (together with the images) in addition to the ASPX code.
the Telerik team